Sometimes Cisco written exams can throw a bit of a curve ball at students when it comes to the questions that can creep into the overall pool of queries. One way in which this can happen is when Cisco asks about a technology or two that is not supported on the current equipment that Cisco is using in the practical lab exam for the same track. Currently we know that for the Version 4.0 of the CCIE R&S exam, Cisco features the following:

• 1841 series routers – IOS 12.4(T) – Advanced Enterprise Services
• 3825 series routers – IOS 12.4(T) – Advanced Enterprise Services
• Catalyst 3560 Series switches running IOS version 12.2 – Advanced IP Services

Correctly so, students tend to study for the written exam against the backdrop of these Cisco devices and Operating Systems. That is a fine idea, but let us be sure to be ready for some features here and there there are not in the scope of our lab equipment.

In this post, I want to discuss Bidirectional Forwarding Detection (BFD) as this feature could very well find its way into a Cisco written exam on the subject of Routing and Switching. This technology is found on Cisco 6500/7600 series routers, as well as 12000 series and Carrier Routing System (CRS-1 Routers).

What is the point of this technology? Like so many protocols and techniques in modern Cisco networking, Bidirectional Forwarding Detection seeks to speed up routing protocol convergence. How does BFD seek to accomplish this? BFD focuses on the ultra-fast detection of node or link failures in the routing infrastructure.

What is the typical approach for the detection of a link or node failure? It is for some type of Hello or Keepalive mechanism to be used at Layer 3. In fact, we have seen these typical mechanisms attempt to evolve by permitting the use of sub-second intervals, as opposed to the long standing multi-second intervals that worked just fine in non mission critical data networks.

BFD operates in a similar fashion, except the fast link hellos are accomplished at Layer 2 instead of the traditional Layer 3. Why is this so exciting? It is not just the fact that there can be blindingly speedy detection of a failure, but also the fact that the CPU impact of the BFD process ends up being much less compared to other Layer 3 fast hello approaches. In testing accomplished by Cisco Systems, network devices running 100 concurrent BFD sessions experienced an increase in CPU utilization of a mere 2%.

For Bidirectional Forwarding Detection to operate correctly in your network environment, you obviously need to use the Cisco Feature Navigator (cisco.com/go/fn) and ensure that you are running the correct hardware and software version for full feature support. This feature does indeed require the cooperation of your Layer 3 protocols, and the great news is that Cisco implementations of EIGRP, IS-IS, and BGP, as well as such important support protocols like HSRP all support Bidirectional Forwarding Detection now.

Thanks for reading this blog post here at blog.ipexpert.com, and should you encounter this Cisco technology in your written, you are now MORE than ready for it! Continue to enjoy those studies!

Should you want more information on BFD at this time – here is a Cisco Documentation Link:

http://www.cisco.com/en/US/docs/ios-xml/ios/iproute_bfd/configuration/12-4t/Bidirectional_Forwarding_Detection.html

Anthony Sequeira CCIE, CCSI
Twitter: @compsolv
Facebook: http://www.facebook.com/compsolv

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UDLD is a Cisco proprietary feature that seeks to eliminate links the can either send or receive traffic, but cannot do both. For example, it can be quite common in Fiber links that a switch can send frames over the connection just fine, but the switch is not able to receive return frames.  Such a unidirectional link condition can be devastating for Spanning Tree Protocol (STP) of course, since a switch could fail to receive BPDUs and incorrectly converge and create a loop in the network.

UDLD functions by the neighbor switches sending specialized frames to a reserved MAC address on each device. The devices look for their returned ID in the frames from the neighbor. There is a normal mode of operation with the feature that serves to simply notify an administrator that the unidirectional link condition could be present. The aggressive mode of operation actually error disables the port when the condition is detected.

Like many Layer 2 features, UDLD can be enabled globally on a Cisco switch, or it can be enabled under a specific interface(s). When the feature is enabled globally, it only effects fiber ports. The command syntax is as follows:

udld {aggressive | enable |message time message-timer-interval}

The interface level command is:

udld port {aggressive |disable}

In an earlier post on LoopGuard, we mentioned how LoopGuard can catch issues that are related to software type problems on a switch and prevent a loop in a wider variety of circumstances. You should realize that UDLD is preferred for catching problems within EtherChannel configurations. While LoopGuard would block an entire EtherChannel bundle in the event of problems, UDLD can just disable the flawed link in the bundle.

For your written exam, it is also important to realize that this UDLD feature can be used to correct port mismatch errors that appear in the show cdp neighbors output as a result of miswirings.

Anthony Sequeira CCIE, CCSI
Twitter: @compsolv
Facebook: http://www.facebook.com/compsolv

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In this ongoing series here at blog.ipexpert.com, we are going to answer the most common questions CCIE instructors hear. Here is the latest:

Question: Am I penalized for over-configuration in the lab exam?

Answer: This is another one of those great questions, especially when you consider the fact that the grading for the lab exam is quite complex. Depending on what track you are discussing, the lab is graded by a computer script, a human, or a combination of both. Given this fact, students begin to suspect that the grading is some mysterious “black art”, that might harshly penalize for the slightest deviation from the proctor’s expectations with a task.

I like to answer this question for students with an example. Say you get the task below:

Sample Task 1 – Switching

1.3 Trunking

Create a standards-based trunk between SW1 and SW4 according to the Layer 2 diagram provided.

2 pts

I recommend that students ask themselves the question here –  how would the proctor write a script to grade this task? I think they would issue the SHOW INTERFACE TRUNK command on each device. In your mind, run through the parameters that must exist.

• Correct two devices
• Correct two interfaces
• UP/UP status
• 802.1Q trunk established

If these parameters are met – you just achieved the 2 pts.

Here are three different configurations (from just one of the two devices) that get the full two points.

Solution 1

switchport trunk encapsulation dot1q
switchport mode trunk

Solution 2

switchport trunk encapsulation dot1q
switchport mode trunk
switchport nonegotiate

Solution 3

switchport trunk encapsulation dot1q
switchport mode trunk
switchport nonegotiate
switchport trunk allowed-vlan 100,200,300,400,500,501,502

Always ask yourself two questions:

1. Could this additional configuration I am about to add help me gain these points?
2. Could this additional configuration I am about to add potentially cost me here or elsewhere in the lab?

If your answers are YES and NO respectively, then you can certainly consider this “additional” configuration. Notice that Solution 3 comes very close to a NO and YES answer respectfully and should be frowned upon as a result.

Another great rule of thumb in this regard – “do what they ask for, nothing more, nothing less!”

Anthony Sequeira CCIE, CCSI
Twitter: @compsolv
Facebook: http://www.facebook.com/compsolv

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A friend told me that I should check out the text Emotional Intelligence 2.0. As I was reading this book, I quickly realized how practical it can be for CCIE candidates. You see Emotional Intelligence is all about your ability to recognize and control your emotions and to understand the impact that they can have on your life.

You see, we are all familiar with IQ. This is a measure that can be assistance to judge how quickly and efficiently we can learn to pass the CCIE. But what about EQ. This is our Emotional Intelligence rating. This can be very important in the pursuit of CCIE. Remember my cornerstones for success?

-Tech Knowledge

- Psychological State

- Physical Wellness

- Strategy

Certainly IQ impacts your technological knowledge, but think about the impact that Emotional Intelligence can have on your psychological state. And remember, the cornerstones all impact each other. For example, if your emotions are out of control and your psychological state is ruined, it can effect all three of the others.

What are the emotions that we need to watch out for in this pursuit?

• Sad – we can feel lonely and isolated from family and friends as we immerse ourselves in study
• Angry – should we experience a NOT PASS this emotion can be powerful
• Afraid – we may be paralyzed with fear regarding a NOT PASS
• Ashamed – many experience this after a NOT PASS event

As I read more of this text, I will be sure to share what tools we should be able to use in our pursuit of CCIE.

Anthony Sequeira CCIE, CCSI
Twitter: @compsolv
Facebook: http://www.facebook.com/compsolv

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